One of the most common mistake is thinking that routers and modem are same which in fact are two different terminology. Though a router can be modems but not always and all modems are also not routers.

Routers: They separate two networks and decide what ports to use and also determine what ip to assign to a internal network. And also what path to take to deliver a packet. They decide all these things on basis of IP private and public both.They may have a in built modem to encode signals into appropriate form like waves, optics, current or decode signals into meaningful form.

Modem: They are used to encode signals or decode signals . It must be noted signals may not always be in form we see in net. Modem is used in any electronics communication like telephone,fm radio or television. What modem means? to modulate a signal at sender's side i.e. change its form and demodulate a signals i.e. give them back into receiver's side in appropriate form. Though a modem may be inbuilt in these so that you don't have to purchase it. When talking about internet modems they have router too now. But in case of cable they have bridge mostly.

Bridges: They separate two networks but they do so with help of MAC address.


Hubs and Repeaters: Hubs connect network lines ( correct terms is nodes). Repeaters ( they are called sometime active hubs)are a kind of hub which amplifies signals.


Switches: Well they are a marketing terms more than any real devices. though some define them as hub having many ports and can change from ont to another which again is cover by all of the above definitions.

Brouter : Bridge+Router as many wireless router are which enables mac filtering.